This invention relates to fiber batts. More particularly, it relates to fiber batts which are particularly useful as thermal insulators, as oil and water separators, and in controlled release applications.
In the late 1960s, Esso (now Exxon) Research and Engineering Company developed a process for forming fiber batts by melt blowing a polymer through a specifically structured die and collecting the fibers on a substrate. An example of the Exxon process is disclosed in U.S. Pat. No. 3,684,415.
The Exxon melt blowing process can be better understood in reference to FIG. 1, which shows, in a general form, an apparatus used in the Exxon process, and to FIG. 2 which shows, inter alia, a useful die head. Turning now to FIG. 1, polymer chips such as, for example, polypropylene, are loaded into extruder 10, where they are heated until the polymer is transformed into a liquid. The extruder screw forces the polymer through die 12 which is also pneumatically connected to blower 14 through air heater 16.
As can be seen from FIG. 2, the molten polymer passes through bore 18 of die head 12. The die head includes a plurality of holes therein (not shown) for providing multiple filaments. The heated air from blower 14 passes through chambers 20 and 22, and the hot air and molten polymer meet at junction 24. Cool air passes along the outer surfaces 26 and 28 of the die head, and strikes the blown fibers just past junction 24. The streams of hot and cool air will draw the filaments. Depending on the flow rate of the air, the filaments can be overdrawn and broken, forming short filaments.
Turning again to FIG. 1, the fibers strike take-up screen 30, which may be rotated. The fibers accumulate on top of each other, and as the fibers hit the take-up screen, they are still in a partial molten form, and thus stick together, forming a batt. The batt then may be wound by means of a take-up spool.
Some of the uses which Exxon suggests for the polypropylene batt are as a filtration media, as an absorbent, as a cigarette filter, as well as other uses.
Fibrous batts of synthetic polymer material made by other processes have become popular for several uses, in particular for thermal insulation in garments and sleeping bags. Recently, very thin batts have been developed which provide excellent insulation properties and are thus very popular in the fashion industry. A leading example of this type of thin insulating batt is a product manufactured by Minnesota Mining & Manufacturing Company called Thinsulate. The Thinsulate material, together with the method of manufacture, is described in U.S. Pat. No. 4,118,531. Thinsulate is a mixture of microfibers and crimped bulky fibers, which produces a lofty resilient web having high thermal resistance per unit thickness, as well as light weight. These fibers are standard solid core polymers in staple form. Complicated tangling of the microfibers and the larger bulky fibers provide for dead air among the fibers, resulting in good insulation properties.
Another example of one of a new insulating batt is shown in U.S. Pat. No. 4,304,817, assigned to E. I. DuPont de Nemours & Company. The DuPont patent shows a fiber-filled blend made into a batt, wherein the fibers are heat-bonded to one another. Very low denier fibers are utilized, together with a binder fiber, so that the batt is relatively thin for its particular thermal characteristics.
Another new insulating material is called Eizac, developed by Teijin Ltd., of Japan. The Eizac is a nonwoven fabric made by a so-called polyester burst fiber process. Each fiber includes dead air in the fiber itself in elongated channels through the core of the fibers.
Many of the above described batts have several drawbacks for use as a thermal insulation. Some of the fibers are hydrophilic; that is, they absorb moisture, which increases the thermal conductivity. Also, many of them appear to be very difficult to manufacture. Furthermore, when the above described 3M and DuPont insulation batts are subjected to load, as, for example, on the bottom side of a sleeping bag, the batt collapses, and the thermal insulation qualities are substantially decreased.